Electrical transformers are known to degrade and fail due to aging, thermal and electrical stresses. When electrical transformers degrade and fail their insulation material—oil—breaks down and generates certain gases commonly referred to as “fault gases” which are dissolved in the degraded oil. Such fault gases may include hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6).
It is well known in the transformer industry that the amount and nature of fault gases can be used to identify the type and severity of the fault in the transformer. For example, hydrogen is often associated with low energy electrical discharge (corona) while acetylene is related to high energy arcing (IEEE Std C57.104 —Guide for the Interpretation of Gases generated in oil-immersed transformers).
Until now, utilities throughout the world have typically relied upon performing a dissolved gas analysis in a laboratory to check for fault gases, and this is typically only done once or twice a year. This practice may be effective for slow evolving faults, but it is not adequate to prevent fast evolving faults which often lead to catastrophic failure and significant damage to a transformer and other assets. And, in fact, there are many documented cases of critical transformer failures which have occurred catastrophically within days or even hours after being energized and/or after the onset of an increasing change in gas production.
Accordingly, there has been a long felt and significant need for a reliable and cost effective method and apparatus which is capable of continuously and quantitatively detecting and monitoring the concentration of key fault gases dissolved in insulating oil.
Although the ideal sensor system for measuring fault gases in transformer oil in order to avoid failure of transformers should detect all fault gases, and not just one or only a selected few, such an approach may not be practical when the total cost of purchasing and maintenance is taken into consideration. The detection of a very small amount but sudden increase of Acetylene (C2H2), in the hundreds of ppb levels or sub-ppm levels, has been considered by many experts in the field as one of the most reliable indications signaling the fact that a transformer has a degradation problem that can lead to transformer failure. Accordingly, designing a gas sensor system focusing on the detection of ppb or sub-ppm levels of acetylene should be a good compromise for detecting and monitoring transformer health in an asset management program.